This invention relates to sleeve bearings of the type having an oil film or layer between the bearing surface and a journaled member. The invention is particularly applicable to half-shell sleeve bearings used in internal combustion engines in cooperation with crankshafts and connecting rods. However, it will be appreciated that the invention has broader applications and may be used in other environments of this general type.
Engine main and connecting rod bearings in internal combustion engines are subjected to repetitive loads which can ultimately fatigue the bearing. These bearings are disposed in a continuously circulated oil bath and there is a clearance provided between the outer peripheral surface of the journaled member or crankshaft and the inner peripheral bearing surface of the sleeve bearing. This facilitates relative rotation between the parts during normal engine operation and facilitates the creation of an oil film between the parts which acts as a load supporting medium during engine operation. The hydrodynamic wedge effect of the oil causes the shaft or journaled member to float on an oil film as a result of there being a difference between the shaft and bearing radii, i.e., a clearance. The oil in the clearance provides lubrication and cooling. It has been shown that the oil film pressure developed in such bearings increases with increased bearing clearance. Bearings exposed to higher pressures fatigue sooner or to a greater extent than bearings exposed to lower pressures. A greater clearance provides a greater oil film pressure and a greater oil film pressure causes the bearing to fatigue faster. It seemingly would be a mere matter of reducing the oil film clearance to reduce the oil film pressure to increase the bearing life. The clearance cannot simply be reduced, however, as that would reduce the lubrication and cooling causing the bearing to run hotter and possibly burn up during operation.
The subject invention provides an improved sleeve bearing having a bearing surface with a first portion extending circumferentially on a constant radius which would be in close clearance or reduced clearance with the journaled member and having a second circumferential portion disposed outside the constant radius to provide a greater clearance. The bearing area of the reduced clearance is in close proximity to the journaled member during the high load portion of each revolution.